This invention relates to the simultaneous control of several individual chiller units within a system that is processing chilled coolant via common supply and return lines. In particular, this invention relates to the control of a number of different chiller units each having their own respective dedicated control units.
Multiple chillers on a common coolant loop are subjected to the same entering coolant temperature at approximately the same time. The chillers are typically required to maintain the leaving coolant at the same temperature. This causes the individual units to simultaneously start or stop their compressors at the same time. This leads to unnecessary and at times excessive demands on electrical power consumption and excessive compressor cycling in order to provide the chilling of the coolant perceived to be necessary. In this regard, each individual chiller unit having its own particular compressor stages and control unit is trying to activate the perceived number of compressor stages necessary to achieve the desired chilling without regard to what may be happening elsewhere. This often produces an over reaction.
What is needed is a hierarchial control system which allows individually controlled units to provide normal control functions while at the same time supervising reaction by the individual chiller units to maintain the leaving coolant temperature at same predefined level.